The present invention relates to an optical recording medium, particularly to a high-density recordable optical recording medium.
At present, the organic materials suitable for the recording layer of recordable compact disks (often referred to as CD-R) are mainly classified into three categories: cyanine dyes, phthalocyanine dyes and azo dyes. These dyes commonly have a maximal absorption at a wavelength of 650 nm to 750 nm in the visible light range. As a major function, the dyes absorb a laser beam of 780 nm and then convert it into thermal energy, such that the recording layer changes in its optical characteristics to fulfil the reflectance requirements as set forth in the specification of the compact disk (Red Book). In view thereof, therefore, an organic material having a light absorption at a wavelength outside the wavelength range of the laser beam is needed for the recording layer of the optical recording media. Since 1990s, in order to satisfy the tendency of continued data expansion, all the major CD manufacturers make efforts at the improvements of the recording density of the CDs by decreasing the spaces between the pits and between the tracks and, in the meantime, narrowing the laser beams for reading signal, to avoid the signal cross-talk between the tracks and to raise the discriminated ratio of track length. As a result, almost all the current developments are concentrated at the laser beams with wavelengths of 650 nm and 635 nm. According to experiences, if the laser beams of 650 nm and 635 nm is to be used, the organic recording layer of the recordable optical recording media preferably has a light absorption at a wavelength between 530 nm and 600 nm.
JP 2640219 (issued to Electronic Chemical Industry Enterprise Corporation, Tokyo, Japan) discloses using cyanine dyes in optical recording media. However, due to the limitation of the chemical structures of the dyes, the optical recording medium disclosed therein is only a low-density recording medium suitable for a writing and reading system with a laser beam of 780 nm.
Therefore, the objective of the present invention is to provide a high-density recordable optical recording medium, which is suitable for writing and reading systems with laser beams of 650 nm and 635 nm.
To achieve the above objective, the recordable high-density optical recording medium according to the invention essentially comprises a substrate and a recording layer formed on said substrate, wherein said recording layer contains at least one laser beam absorbing dyes of the formula (I) 
wherein Q is phenyl or naphthyl substituted with C1-4alkoxy; R1 and R2, independently of each other, are C1-8alkyl; Y is hydrogen or C1-4alkoxy; and Xxe2x88x92 is an anion.
For the purpose of the invention, the recording layer preferably contains the laser beam absorbing dyes of the formula (I), wherein R1 is methyl, ethyl, propyl or butyl; R2 is methyl, ethyl, propyl or butyl; Y is hydrogen or methoxy; and Xxe2x88x92 is a perchlorate ion or hexafluorophosphate ion.
Preferably, the recording layer of the recordable high-density optical recording media according to the invention contains the laser beam absorbing dye of the formula (I), wherein Q is naphthyl substituted with methoxy; R1 is methyl, ethyl, propyl or butyl; R2 is methyl, ethyl, propyl or butyl; Y is methoxy; and Xxe2x88x92 is a perchlorate ion.
More preferably, the recording layer of the recordable high-density optical recording media according to the invention contains the laser beam absorbing dye of the formula (I), wherein Q is phenyl; R1 is methyl, ethyl, propyl or butyl; R2 is butyl; Y is hydrogen; and Xxe2x88x92 is a hexafluorophosphate ion.
Particularly preferably, the recording layer of the recordable high-density optical recording media according to the invention contains the laser beam absorbing dyes selected from the following compounds or the combinations thereof:
2-(3xe2x80x2-(1xe2x80x3, 3xe2x80x3, 3xe2x80x3-trimethyl-6xe2x80x3-methoxy-benzo[e]indole)-propenyl)-1,3,3-trimethyl-6-methoxy-benzo[e]indole perchlorate;
2-(3xe2x80x2-(1xe2x80x3-ethyl-3xe2x80x3, 3xe2x80x3-dimethyl-6xe2x80x3-methoxy-benzo[e]indole)-propenyl)-1-ethyl -3,3-dimethyl-6-methoxy-benzo[e]indole perchlorate;
2-(3xe2x80x2-(1xe2x80x3-propyl-3xe2x80x3, 3xe2x80x3-dimethyl-6xe2x80x3-methoxy-benzo[e]indole)-propenyl)-1-ethyl-3,3-dimethyl-6-methoxy-benzo[e]indole perchlorate;
2-(3xe2x80x2-(1xe2x80x3-butyl-3xe2x80x3, 3xe2x80x3-dimethyl-6xe2x80x3-methoxy-benzo[e]indole)-propenyl)-1-butyl-3,3-dimethyl-6-methoxy-benzo[e]indole perchlorate;
2-(3xe2x80x2-(1xe2x80x3, 3xe2x80x3, 3xe2x80x3-trimethylindole)-propenyl)-1-butyl-3,3-dimethyl-benzo[e]indole hexafluorophosphate;
2-(3xe2x80x2-(1xe2x80x3-ethyl-3xe2x80x3, 3xe2x80x3-dimethylindole)-propenyl)-1-butyl-3,3-dimethyl-benzo[e]indole hexafluorophosphate;
2-(3xe2x80x2-(1xe2x80x3-propyl-3xe2x80x3, 3xe2x80x3-dimethylindole)-propenyl)-1-butyl-3,3-dimethyl-benzo[e]indole hexafluorophosphate; and
2-(3xe2x80x2-(1xe2x80x3-butyl-3xe2x80x3, 3xe2x80x3-dimethylindole)-propenyl)-1-butyl-3,3-dimethyl-benzo[e]indole hexafluorophosphate.
The present invention is now described in more detail with reference to the following examples.